The present invention relates to a display driver and method for operating an emissive light video display.
Status displays are an important feature of electronic devices such as cellular telephones, global positioning systems (GPS), CD players, video cameras, digital cameras, conventional cameras, hybrid cameras and other devices. Status displays are used to inform the user of such a device about conditions that may impact the operation of the device. Examples of status displays include displays that indicate cellular telephone signal strength, battery status, and other warnings. These displays are typically active whenever the device is active. Because these displays are often in use, it is necessary that these displays consume little power.
In the prior art, it is known to use Light Emitting Diodes, LEDs, and Liquid Crystal Displays, LCDs to present status information to the user of a hand held electronic device. These LEDs and LCDs are typically arranged or shaped in the form of icons that symbolically represent the status of the device. Using such displays, the status of the device can readily be ascertained by observing whether the LEDs or LCDs are active. Such LEDs and LCDs draw little power and are simple to operate. However, it will be appreciated that at least one separate LED or LCD must be incorporated into the portable electronic device for each status display. This increases the size and weight of the portable device, typically reducing the convenience and portability of the device.
In the prior art, it is also known to provide video displays in hand held and portable devices. Such video displays are typically formed from a two dimensional matrix of image forming elements. In a preferred form of video display known as the Emissive Light Display, ELD, the image forming elements comprise discrete light emitting elements. An image to be displayed using an ELD is electronically captured and encoded into illumination values. The illumination values are written to the elements of the display and the elements illuminate at an intensity level that is called for in the illumination values. Variations in the intensity of light emitted by the elements create a contrast pattern that forms the image on the display.
It will be appreciated that video displays can convey images including icons, graphics, text, still and motion images. This enables portable devices to communicate with users in a very effective fashion. Accordingly, video displays are increasingly being incorporated into portable electronic devices.
However, the video displays of the prior art have consumed too much power to permit such video displays to be operated continuously. A certain portion of the power consumed is used to cause the elements of the display to emit light. Traditionally, it has taken substantial amounts of power to cause the elements of ELDs to emit light. However, with the advent of the Organic Light Emissive Display (OLED) it has become possible to substantially reduce the amount of power consumed in causing the elements of the display to emit light.
The remaining portion of the power consumed in the operation of a video display is used by the electronic controls that control the elements of the display. These controls are collectively known as a display driver. The prior art has not provided a display driver or method for operating an OLED that is efficient enough to permit the near continuous operation of the OLED for the purposes of sustaining status displays.
In the absence of such a display driver, it has become common for portable electronic devices that incorporate video displays to also incorporate separate LED and LCD displays to present status information. It will be appreciated that incorporating such a dual display scheme into a portable electronic devices increases the number of components of the device, the cost of designing the device, and the size and weight of the device. These factors increase the cost of portable electronic devices that incorporate both video and separate LED or LCD status displays.
U.S. Pat. No. 5,977,704 recognizes that a need exists for a single display to present both video and status information. To meet this need, the ""704 patent shows a single Organic Light Emissive Display (OLED) having both a video display region and an icon region. The main limitation of this solution is that it is expensive to design and manufacture such an OLED. For example, any modification to the form, number, or arrangement of icons requires a modification to the physical structure of the display device. Accordingly, a display device designed for one product in accordance with the ""704 patent will not be readily adaptable for use in a second product.
Thus, what is needed is a display driver and method for displaying both icons and video images and that does not require the use of custom combination displays.
U.S. Pat. No. 4,823,121 represents one effort to reduce the power consumed in generating an image using a light emissive display. The ""121 patent teaches a display control circuit for producing illumination values for controlling the illumination intensity level of light emissive display elements in an Electro-Luminescent (E-L) display panel. The ""121 patent teaches that each of the illumination values associated with a horizontal row of elements in an E-L display is to be written to a shift register and examined while in the shift register. If no element in the row is to be illuminated, the driver can omit the step of transmitting the illumination values to the elements in the row and the step of applying a maintenance charge to the row of elements. The ""121 patent, however, still requires that the display driver generates illumination values for all of the elements in the display, to examine the illumination values for each row to determine whether to write illumination values to each of the elements 14 in the display and to determine whether to apply a maintenance charge to the row of elements.
Thus, the forgoing needs are not met by the prior art.
According to a feature of the present invention, a method is provided for using a two-dimensional matrix of light emitting elements to display an image electronically encoded in the form of illumination values. An array of elements including less than all of the elements in the matrix to display the image is defined. A pixel rate for writing the illumination values for the elements in the array is determined, and a sweep signal having the illumination values for the elements in the array is generated, where the sweep signal writes illumination values for the elements in the array at the determined pixel rate.
According to another embodiment of the present invention, a display driver generates an image encoded in the form of illumination values. The driver includes an image source and a controller receiving the image from the image source, said controller being adapted to (1) define an array of elements including fewer than all of the elements in the matrix for display of the image (2) determine a pixel rate for writing illumination values to the array of elements, and (3) generate images by writing illumination values to the elements in the array at the pixel rate.